Room and Pillar

An underground mining method in which the target material is cut away in a grid of open 'rooms', while regularly spaced 'pillars' of unworked rock are deliberately left standing to hold up the roof above — one of the two basic philosophies of underground extraction, alongside total-extraction methods like longwall mining, and the method behind some of the largest man-made underground spaces in Britain.

Historical usage

Room-and-pillar working — called 'pillar and stall' or 'bord and pillar' in different British coalfields — has genuinely ancient roots, in use across Europe from at least the 13th century and adopted for British coal mining from its earliest large-scale days in the 18th century. It was never confined to coal: the same basic method was used wherever a mineral deposit was thick and roughly horizontal enough to be worked as a grid of chambers rather than followed as a narrow vein. Cae Coch's pyrites were worked as pillar-and-stall, with pillars 2-3 yards square spaced 8-10 yards apart; Combe Down's Bath stone was cut by hand saw and pick into parallel chambers; and Winsford's rock salt is worked in galleries around 20 metres wide and 7.5 metres high, among the largest room-and-pillar openings anywhere in the country. Mechanisation from the late 1920s, reaching full effect by the late 1940s, sped up the method considerably without changing its basic principle.

How it worked

Working proceeded outward from an access point in a regular grid pattern, cutting away the target material in 'rooms' while leaving 'pillars' of the same material standing at calculated intervals to carry the weight of everything above; the size and spacing of the pillars depended on the strength of the material being worked and the depth and weight of the overlying ground, with weaker rock or deeper workings demanding larger, more closely spaced pillars.

Why it was used

Compared with total-extraction methods, room and pillar left a stable underground void behind it rather than a collapsing one, reducing the risk of surface subsidence, and — because pillars, roadways and rooms could all be worked with fairly simple equipment — it suited both hand-worked 18th- and 19th-century operations and, later, mechanised ones equally well.

Risks & limitations

A method that depends on leaving enough material behind to hold the roof up only works if that discipline is maintained: at Combe Down, 19th-century quarrymen frequently cut pillars back for extra stone once the site's original disciplined operator was no longer overseeing the work, weakening the very supports the whole system depended on. The resulting instability became so severe that a major stabilisation scheme running from 2004 to 2009 had to pump some 600,000 cubic metres of foamed concrete into 25 hectares of the old workings, at a cost of around £150 million, to save the houses built above — the largest single application of foamed concrete ever undertaken in the UK. Retreat mining, deliberately removing pillars themselves as a working is abandoned to recover the last of the material, recovers more of the resource but sharply increases the risk of subsidence, especially in shallow workings.

Regional variation

Used wherever a deposit suited it rather than tied to one region — British coalfields generally called it 'bord and pillar' or 'pillar and stall', while stone and salt workings more often used 'room and pillar' itself, but the terms describe the same basic method under different regional and industry vocabulary.

Images

Mines associated with this term

Included only where MineArchive's own research gives a reasonable evidential basis — not every mine where this might plausibly apply.

• Box Quarry — Wiltshire (well documented example)
  Bath stone was worked by room-and-pillar mining, leaving the largest stone mine in the country — around 600 acres of interconnecting galleries and pillars.
• Cae Coch Sulphur Mine — Conwy (well documented example)
  Pyrites ore was worked by the pillar-and-stall method, with pillars 2-3 yards square spaced 8-10 yards apart.
• Combe Down Stone Mines — Somerset (well documented example)
  Bath stone was worked by the room-and-pillar ('pillar and stall') method, cut by hand saw and pick — later instability from pillar-robbing required a £150 million stabilisation scheme.
• Winsford Rock Salt Mine — Cheshire (well documented example)
  Rock salt is worked in room-and-pillar galleries around 20 metres wide and 7.5 metres high, among the largest such openings in the country.

Sources

1. (secondary) Foamed Concrete Mass Infill, Combe Down Mines, Bath, Somerset — Foamed Concrete Ltd
2. (secondary) Retreat mining — Wikipedia
3. (secondary) Room and pillar mining — Wikipedia
4. (secondary) The Stabilisation of Combe Down Stone Mines — Museum of Bath Stone

Record created: 22 August 2026 · Last researched: 22 August 2026